Vehicle headlamps are designed to illuminate an area in front of the vehicle by projecting high intensity beams of light in prescribed patterns over selected portions of a roadway. Vehicles are generally equipped with a first pair of high beam headlamps and a second pair of low beam headlamps. The high beam headlamps are designed to illuminate the entire width of the roadway in front of the vehicle and a greater length of roadway than that illuminated by the low beam headlamps. The low beam headlamps project a pattern of light downward and to the right of the high beam illumination pattern so as not to temporarily blind an oncoming motorist. In some vehicles, high and low beam illumination patterns are projected from the same headlamp using different filaments.
In order to produce the desired illumination pattern for both the high and low beams, the headlamps must be properly aimed. Standards for headlight aiming and illumination patterns are prescribed by industrial groups, such as the Society for Automotive Engineers (SAE), and by governmental agencies. Generally, different aiming and illumination pattern standards have been prescribed for different geographical areas, such as North America and Europe, making it difficult to produce universally applicable device for checking the aim of vehicle headlamps.
Methods and devices for aiming and determining misalignment of vehicle headlamps are known. Examples of these known methods and devices are shown in Preston U.S. Pat. No(s). 3,386,333 and 3,467,473; Ishakawa et al. U.S. Pat. No. 4,647,195; and Hopkins et al. U.S. Pat. No. 4,948,249. Each of these references discloses both a method and a device for testing the aim of an automotive headlamp.
Preston U.S. Pat. No. 3,386,333 describes means for properly aiming the illumination pattern of a low beam headlamp by properly determining and locating the edge of a high intensity zone of the low beam illumination pattern on a headlamp target board. Light sensitive devices or photoreceptors are positioned on the target board. As an operator adjusts the headlamps to scan the light sensitive devices or photoreceptors, the proper aiming of the headlamps will be achieved when meters indicate a minimum value.
Also to Preston U.S. Pat. No. 3,467,473, discloses a photoelectric headlamp aiming apparatus and method in which a high intensity zone of the low beam headlamps of a vehicle may be properly positioned by scanning the high intensity zone over an aiming board. The aiming board includes photoreceptors positioned relative to a properly positioned edge of the high intensity zone, and computing means for determining the rate of change of the intensity curve as the edge of the high intensity zone is scanned over the photoreceptors. When this rate of change is maximized, the high intensity zone of the low beam headlamps is properly positioned and aimed.
Ishikawa's headlamp testing device and method, as shown in U.S. Pat. No. 4,647,195, involves the steps of shining the low beam of the vehicle headlamp onto a screen and determining the position of the geometrical center of a closed area of illuminance. A cut off line cross point is determined from the position of the geometrical center and a predetermined amount of offset, and a presumption line is determined from the cut off line cross point. The presumption line is displayed together with a mark which indicates an area within which the cross point should fall for a headlamp having a correctly aligned beam axis.
Hopkins U.S. Pat. No. 4,948,249 shows another method and apparatus for determining proper headlight aiming, in which SAE test conditions are simulated. The light beam of the headlamp is focused on a screen having a sensor for sensing the light intensity in each cell of a matrix of cells which overlies the focused light beam. The sensor produces an analog or digital electrical signal for each cell which indicates the cell location and the intensity of light within that cell. Analog signals are preferably digitized. The digital signals are then manipulated by computer to determine headlight aiming accuracy, to correct inaccurate aiming, and to describe the illumination pattern of the headlight.
While the described methods and devices for aiming and determining misalignment of vehicle headlamps are useful in checking and correcting the aim of the headlamps, each is limited in its application. The known methods and devices are either not readily adaptable to changing aiming standards because they sense light at a limited number of discrete locations in the headlamp beam, or they are incapable of checking headlamp aim under actual, and not merely simulated, SAE test conditions. None of the foregoing patents discloses a universally adaptable and fully portable device for checking the aim of a vehicle headlamp under actual SAE test conditions, and for graphically displaying the difference between the actual aim of a vehicle headlamp and the aim of a headlamp having true alignment.
It is therefore an object of the present invention to provide a system for checking the aim of a vehicle headlamp under actual SAE conditions which is adaptable for use with all sizes of vehicles.
It is another object of the invention to provide a portable system for determining if the aim of a vehicle headlamp is within prescribed standards, and for providing a visual indication of the difference between the aim of a properly aligned headlamp and the actual aim of the headlamp.
It is a further object of the invention to provide a method for checking the aim of a vehicle headlamp under actual SAE conditions using a portable system which is universally applicable for use with all sizes of vehicles.